Just Command Runner

Overview

Expert guidance for Just, a command runner with syntax inspired by make. Use this skill for creating justfiles, writing recipes, configuring settings, and implementing task automation workflows.

Key capabilities:

• Create and organize justfiles with proper structure

• Write recipes with attributes, dependencies, and parameters

• Configure settings for shell, modules, and imports

• Use built-in constants for terminal formatting

• Implement check/write patterns for code quality tools

Quick Reference

Essential Settings

set allow-duplicate-recipes # Allow recipes to override imported ones set allow-duplicate-variables # Allow variables to override imported ones set shell := ["bash", "-euo", "pipefail", "-c"] # Strict bash with error handling set unstable # Enable unstable features (modules, script attribute) set dotenv-load # Auto-load .env file set positional-arguments # Pass recipe args as $1, $2, etc.

Common Attributes

Attribute Purpose

[arg("p", long, ...)]

Configure parameter as --flag option (v1.46)

[arg("p", pattern="…")]

Constrain parameter to match regex pattern

[group("name")]

Group recipes in just --list output

[no-cd]

Don't change to justfile directory

[private]

Hide from just --list (same as _ prefix)

[script]

Execute recipe as single script block

[script("interpreter")]

Use specific interpreter (bash, python, etc.)

[confirm("prompt")]

Require user confirmation before running

[doc("text")]

Override recipe documentation

[positional-arguments]

Enable positional args for this recipe only

Recipe Argument Flags (v1.46.0+)

The [arg()] attribute configures parameters as CLI-style options:

Long option (--target)

[arg("target", long)] build target: cargo build --target {{ target }}

Short option (-v)

[arg("verbose", short="v")] run verbose="false": echo "Verbose: {{ verbose }}"

Combined long + short

[arg("output", long, short="o")] compile output: gcc main.c -o {{ output }}

Flag without value (presence sets to "true")

[arg("release", long, value="true")] build release="false": cargo build {{ if release == "true" { "--release" } else { "" } }}

Help string (shown in just --usage)

[arg("target", long, help="Build target architecture")] build target: cargo build --target {{ target }}

Usage examples:

just build --target x86_64 just build --target=x86_64 just compile -o main just build --release just --usage build # Show recipe argument help

Multiple attributes can be combined:

[no-cd, private] [group("checks")] recipe: echo "hello"

Built-in Constants

Terminal formatting constants are globally available (no definition needed):

Constant Description

CYAN , GREEN , RED , YELLOW , BLUE , PURPLE

Text colors

BOLD , ITALIC , UNDERLINE , STRIKETHROUGH

Text styles

NORMAL

Reset formatting

BG_*

Background colors (BG_RED, BG_GREEN, etc.)

HEX , HEXLOWER

Hexadecimal digits

Usage:

@status: echo -e '{{ GREEN }}Success!{{ NORMAL }}' echo -e '{{ BOLD + CYAN }}Building...{{ NORMAL }}'

Key Functions

Require executable exists (fails recipe if not found)

jq := require("jq")

Get environment variable with default

log_level := env("LOG_LEVEL", "info")

Get justfile directory path

root := justfile_dir()

Recipe Patterns

Status Reporter Pattern

Display formatted status during multi-step workflows:

@_run-with-status recipe *args: echo "" echo -e '{{ CYAN }}→ Running {{ recipe }}...{{ NORMAL }}' just {{ recipe }} {{ args }} echo -e '{{ GREEN }}✓ {{ recipe }} completed{{ NORMAL }}' alias rws := _run-with-status

Check/Write Pattern

Pair check (verify) and write (fix) recipes for code quality tools:

[group("checks")] @biome-check +globs=".": na biome check {{ globs }} alias bc := biome-check

[group("checks")] @biome-write +globs=".": na biome check --write {{ globs }} alias bw := biome-write

Full Check/Write Pattern

Aggregate all checks with status reporting:

[group("checks")] @full-check: just _run-with-status biome-check just _run-with-status prettier-check just _run-with-status tsc-check echo "" echo -e '{{ GREEN }}All code checks passed!{{ NORMAL }}' alias fc := full-check

[group("checks")] @full-write: just _run-with-status biome-write just _run-with-status prettier-write echo "" echo -e '{{ GREEN }}All code fixes applied!{{ NORMAL }}' alias fw := full-write

Standard Alias Conventions

Recipe Alias Recipe Alias

full-check fc full-write fw

biome-check bc biome-write bw

prettier-check pc prettier-write pw

mdformat-check mc mdformat-write mw

tsc-check tc ruff-check rc

test t build b

Inline Scripts

Just supports inline scripts in any language via two methods:

Script Attribute (Recommended)

Use [script("interpreter")] for cross-platform compatibility:

[script("node")] fetch-data: const response = await fetch('https://api.example.com/data'); const data = await response.json(); console.log(data);

[script("python3")] analyze: import json with open('package.json') as f: pkg = json.load(f) print(f"Package: {pkg['name']}@{pkg['version']}")

[script("bash")] deploy: set -e npm run build aws s3 sync dist/ s3://bucket/

Shebang Method

Use #!/usr/bin/env interpreter at the recipe start:

node-script: #!/usr/bin/env node console.log(Node ${process.version}); console.log(JSON.stringify(process.env, null, 2));

python-script: #!/usr/bin/env python3 import sys print(f"Python {sys.version}")

bash-script: #!/usr/bin/env bash set -euo pipefail echo "Running on $(uname -s)"

When to use which:

• [script()]

• Better cross-platform support, cleaner syntax

• Shebang - Traditional Unix approach, works without set unstable

Modules & Imports

Import Pattern

Include recipes from another file:

import "./just/settings.just" import "./just/base.just" import? "./local.just" # Optional (no error if missing)

Module Pattern

Load submodule (requires set unstable ):

mod foo # Loads foo.just or foo/justfile mod bar "path/to/bar" # Custom path mod? optional # Optional module

Call module recipes

just foo::build

Devkit Import Pattern

For projects using @sablier/devkit :

import "./node_modules/@sablier/devkit/just/base.just" import "./node_modules/@sablier/devkit/just/npm.just"

Section Organization

Standard section header format:

----------------------------------------------------------------------------

DEPENDENCIES

----------------------------------------------------------------------------

Common sections (in order):

• DEPENDENCIES - Required tools with URLs

• CONSTANTS - Glob patterns, environment vars

• RECIPES / COMMANDS - Main entry points

• CHECKS - Code quality recipes

• UTILITIES / INTERNAL HELPERS - Private helpers

Default Recipe

Always define a default recipe:

Show available commands

default: @just --list

Dependencies Declaration

Document required tools at the top:

----------------------------------------------------------------------------

DEPENDENCIES

----------------------------------------------------------------------------

Bun: https://bun.sh

bun := require("bun")

Ni: https://github.com/antfu-collective/ni

na := require("na") ni := require("ni") nlx := require("nlx")

Usage: invoke directly in recipes (not with interpolation)

build: bun next build

Note: require() validates the tool exists at recipe evaluation time. Use the variable name directly (e.g., bun ), not with interpolation ({{ bun }} ).

Context7 Fallback

For Just features not covered in this skill (new attributes, advanced functions, edge cases), fetch the latest documentation:

Use context7 MCP with library ID /websites/just_systems-man to get up-to-date Just documentation.

Example topics to search:

• modules import mod

• Module system details

• settings

• All available settings

• attributes

• Recipe attributes

• functions

• Built-in functions

• script recipes

• Script block syntax

Additional Resources

Reference Files

For detailed patterns and comprehensive coverage, consult:

• references/settings.md

• Settings configuration and module system

• references/recipes.md

• Recipe attributes, parameters, dependencies, and prefixes

• references/syntax.md

• Constants, functions, variables, and CLI options

• references/patterns.md

• Established conventions, section organization, helper patterns

Example Templates

Working justfile templates in examples/ :

• devkit.just

• Minimal template importing @sablier/devkit

• standalone.just

• Full standalone template with all patterns

External Documentation

• Official Manual: https://just.systems/man/en/

• GitHub Repository: https://github.com/casey/just

• Context7 Library ID: /websites/just_systems-man

Tips

• Use @ prefix to suppress command echo: @echo "quiet"

• Use + for variadic parameters: test +args

• Use * for optional variadic: build *flags

• Quote glob patterns in variables: GLOBS := ""**/*.json""

• Use [no-cd] in monorepos to stay in current directory

• Private recipes start with _ or use [private]

• Always define aliases after recipe names for discoverability